Silicon nitride plays a major role in the fabrication of semiconductor devices in which the critical dimensions of, as well as positions of, various elements, such as, for example, transistors, resistors, and interconnects, are precisely determined on the wafer and fabricated. Silicon nitride may be used, for example, as a spacer or as a mask. In many circumstances, it is necessary to remove the silicon nitride from the wafer prior to proceeding with further processing. In order to provide adequate throughput for processing the semiconductor devices, the removal of the silicon nitride should be performed as quickly as possible, without damage to regions underlying the silicon nitride and with the desired selectivity to such underlying regions.
In particular, silicon nitride is used as a hard mask for definition of active regions of devices. For example, silicon nitride is utilized in the local oxidation of silicon (LOCOS) process as an oxidation mask. The oxidation mask allows for growth of field oxidation regions between active areas later processed in accordance with conventional techniques, such as for the fabrication of CMOS memory devices. After the field oxidation formation is completed, the silicon nitride hard mask is removed.
However, the field oxide growth process drives hydrogen out of the silicon nitride hard mask which typically has a film composition that may be expressed as Si.sub.x N.sub.y H.sub.z. This reduction in hydrogen concentration of the silicon nitride hard mask causes difficulty to the silicon hard mask removal process, which typically includes the use of a hot phosphoric acid (H.sub.3 PO.sub.4) strip. For example, with hydrogen driven from the silicon nitride hard mask, the speed at which the silicon nitride hard mask is removed by the hot phosphoric acid treatment is substantially decreased.
As a result of the time consuming conventional silicon nitride removal processes, throughput of wafers being fabricated is decreased. Therefore, there is a need in the art for improved silicon nitride removal methods.